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Controllable design of polypyrrole-iron oxide nanocoral architectures for supercapacitors with ultrahigh cycling stability Chunping Xu, Alain Rafael Puente Santiago, Daily Rodríguez-Padrón, Alvaro Caballero, Alina Mariana Balu, Antonio A. Romero, Mario J. Muñoz-Batista, and Rafael Luque ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b02167 • Publication Date (Web): 12 Feb 2019 Downloaded from http://pubs.acs.org on February 14, 2019
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ACS Applied Energy Materials
Controllable Design of Polypyrrole-Iron Oxide Nanocoral Architectures for Supercapacitors with Ultrahigh Cycling Stability Chunping Xu,+a Alain R. Puente-Santiago,+b Daily Rodríguez-Padrón,*b Alvaro Caballero,c Alina M. Balu,b Antonio A. Romero,b Mario J. Muñoz-Batista,b Rafael Luque*b,d [a]
School of Food and Biological Engineering, Zhengzhou University of Light Industry
Zhengzhou, Henan, 450002, PR China
[b]
Departamento de Química Orgánica,Instituto de Química Fina y Nanoquímica, Universidad
de Córdoba, Campus de Rabanales, Edificio Marie Curie (C-3), Ctra Nnal IV-A, Km 396, E14014, Cordoba, España. *D.R.P.:
[email protected], *R.L.:
[email protected] [c]
Departamento de Química Inorgánica e Ingeniería Química, Instituto de Química Fina y
Nanoquímica, Universidad de Córdoba, Campus de Rabanales, Edificio Marie Curie (C-3), Ctra Nnal IV-A, Km 396, E14014, Cordoba, España.
[d]
Peoples Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya str.,
117198, Moscow, Russia.
‡
These authors contributed equally to the work.
Abstract Polypyrrole-modified iron oxide nanomaterials have been synthesized employing a one-step hydrotermal protocol. The influence of the reaction temperature has been investigated by performing the synthesis at four different temperatures (Ppy@Fe2O3-120 °C, Ppy@Fe2O3140 °C, Ppy@Fe2O3-160 °C and Ppy@Fe2O3-180 °C). Synthesized materials exhibited an unprecedentedly peculiar morphology (star/coral reef-like architectures), induced by the 1 ACS Paragon Plus Environment
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presence of pyrrole in the reaction media. Full characterization of the samples revealed the critical influence of temperature on the crystallinity, textural properties and specially on (C+N)/Fe surface ratios in the materials. As-synthesized nanohybrids were integrated into electrodes to construct supercapacitor devices. A effective tuning of the electrochemical features was achieved by controlling the (C+N)/Fe ratio on the surface, strongly dependent on reaction temperature. The best electrochemical performance was reached by Ppy@Fe2O3180 °C nanohybrid, which exhibited a remarkable capacitance value of 560 F g -1 at a current density of 5 A g-1 and an outstanding cycling stability of ca. 97.3% after 20000 cycles of charge-discharge at 40A g-1 was reached. Keywords: iron oxide, pyrrole, nanocoral architectures, supercapacitor, electrochemical performance.
1. Introduction The synthesis of hybrid (nano)capacitors has opened up new horizons towards a deeper study of electrochemical double-layer (EDL) processes at the nanoscale level as well as the opportunity to fabricate more efficient nano-storage systems.1-5 Particularly, the development of redox active nanomaterials bearing pseudocapacitance including metal oxides based nanostructures, has been investigated in recent times. The aforementioned systems undergo fast and reversible surface redox reactions (faradaic reactions), favouring the enhancement of both energy and power densities.6-9 In this sense, nanosized metal oxides structures are highly desirable towards the fabrication of effective supercapacitor electrodes taking advantages of their unique surface properties, which in fact enhance ion diffusion across materials and consequently redox reaction rates.10 A myriad of strategies have been attempted to design supercapacitors
with
manganese,12 cobalt
13
enhanced
electrochemical
properties
fabricated
from
iron,11
or vanadium oxide nanoarchitectures.14 The synthesis of binder-free
nanomaterials,15,16 the modification of metal oxides surfaces with carbonaceous materials or 2 ACS Paragon Plus Environment
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conducting polymers using different approaches such as core-shell,17,18 core-branch19,20 and sandwich structure;21 and most recently the anchorage of biomolecules onto metal oxides surfaces22,23 are among most recently relevant reported examples. Despite these remarkable achievements in the preparation of advanced nanomaterials with improved supercapacitive performances, only a few research studies have addressed to date the possibility to control the electrochemical properties of the synthesized nanoarchitectures by tailoring their structural and/or surface properties. Bearing in mind such concept, Low and coworkers24 have developed a facile synthetic method to tune the morphology of iron oxide nanostructures from 0D nanoparticles, 1D nanorods to 3D self-assembled nanorods, which directly impinges the supercapacitive activity of the obtained nanocapacitors. The development of tunable nanostorage systems therefore constitutes a promising alternative to solve current drawbacks of conventional metal oxides supercapacitor electrodes which include a poor electrical conductivity and cycling stability for a long period of time (usually below 10000 cycles). In this work, polypyrrole coated iron oxide nanocorals (PPy@ Fe2O3) have been successfully synthesized using a simple and effective hydrothermal one-pot approach and employed as high performance supercapacitors with ultrahigh cycling stability. Polypyrrole (Ppy) was chosen due to its high electrical conductivity (10−100 S cm−1)25 and its capacity to enable fast redox reactions for store/charge processes.26 The electrochemical behaviour could be nicely tuned by considering the polypyrrole concentration at the nanostars surfaces, which can be nicely controlled via regulating the temperature of the synthetic route.
2. Experimental Section
Synthesis of PPy@ Fe2O3 nanomaterials: The preparation of the polypyrrole-modified iron oxide nanomaterials was carried out by a one-step hydrothermal treatment employing 3.2 g of Fe(NO3)3·9H2O, 0.4 mL of pyrrole and 40 mL of ethanol. The preparation was conducted in 3 ACS Paragon Plus Environment
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an autoclave system for 12 h at four different temperatures, namely 120 °C, 140 °C, 160 °C and 180 °C, giving rise to Ppy@Fe2O3-120 °C, Ppy@Fe2O3-140 °C, Ppy@Fe2O3-160 °C and Ppy@Fe2O3-180 °C. The final materials were eventually filtered, washed several times with ethanol and dried at 50 °C overnight. The reference pure Fe2O3 sample was synthesized following the same procedure that was employed for the preparation of Ppy@Fe2O3-180 °C, in absence of pyrrole. The preparation of Fe2O3 sample was carried out by a one-step hydrothermal treatment employing 3.2 g of Fe(NO3)3·9H2O and 40 mL of ethanol. The preparation was conducted in an autoclave system for 12 h at 180 °C. The final material was filtered, washed several times with ethanol and dried at 50 °C overnight. Material characterization: The prepared materials were characterized by several techniques including X-ray Diffraction (XRD), N2-physisorption, Thermogravimetric Analysis (TGA), X-ray Photoelectronic spectroscopy (XPS), Transmittion Electronic Microscopy (TEM) and Scanning Electronic Microscopy. XRD experiments were performed in a Bruker D8 Advance Diffractometer (LynxEye detector). XRD patterns were acquired in a 2θ scan range from 10° to 70°. Bruker Diffracplus Eva software, supported by Power Diffraction File database, was employed for phase indentification. N2-physisorption measurements were carried out in a Micromeritics ASAP 2000 equipment. Samples were degassed prior to the analysis for 24 h under vacuum (p
